It is known, in connection with space or utility water heating, to utilize an absorption heating plant which operates with a coolant (refrigerant) and a solvent in which the coolant is soluble with the heat of absorption being recovered. The coolant or refrigerant generally is ammonia while the solvent is generally water and, in addition to these fluids which can have respective circulating paths, a heat-carrying fluid, e.g. steam or hot water, can be provided.
Reference will be made herein to a coolant-rich or coolant-poor solvent to indicate that the solvent is either close to saturation in the coolant or has been practically stripped from the coolant, respectively.
It is known to provide a momovalent alternative absorption heating installation of this type which operates in a heat pump mode above a predetermined ambient temperature and which operates in a direct heating mode at lower temperatures.
In such systems, a condenser is provided for the refrigerant and an absorber is utilized to contact the solvent directly with the coolant, thereby bringing about absorption of the coolant by the solvent. The absorber, therefore, thus serves to convert the coolant-poor solvent into a coolant-rich solvent.
As noted, the system operates with a coolant circulation in which the coolant stripped or driven from the coolant-rich solvent is liquefied or condensed, vaporized by heat exchange with the environment and absorbed by the coolant-poor solvent.
In the heat-carrier circulation, a heat carrier is heated by heat exchange with the condensing coolant and by taking up absorption heat.
Such systems have been found to be practical for single family homes as well as for multifamily dwellings.
The appellation "monovalent alternative" as applied to such a heating unit indicates that the latter operates with only one primary energy source until a predetermined minimum ambient air temperature is achieved in a heat pump mode and below this temperature also can operate in a direct heating mode by the same energy source with direct heating of the heat carrier by this energy source.
An operation of this type is described in German patent document No. 27 58 773 which describes two variants for switching over the apparatus from heat pump mode to direct heating mode. In one case the solvent heated in a heat generator (a flame-type heater) is directly fed to the absorber for transfer of thermal energy to the heat carrier whereas, in the other case, the heated solvent passes successively through the coolant condenser and the absorber in heat exchange with the heat carrier.
Thus, in both cases, the solvent must traverse a number of elements, namely, the absorber, the condenser and the solvent pump, thereby raising the temperatures thereof well above the preferred temperatures during heat pump operation and resulting in considerable heat loss. In addition, heat exchange between the coolant-poor and coolant-free solvent from a high pressure in the stripper to the lower pressure of the absorber will result in a significant cooling of the solvent and thereby reduce the temperature differential between the solvent and the heat carrier in the absorber to diminish the rate of heat transfer therebetween.
It has also been found to be a disadvantage that the coolant-poor solvent traverses the condenser in the direct heating mode. When the system is switched over again to the heat pump mode, the solvent in the evaporator manifests an excessive cold loss. Finally, upon switching over from heat pump mode to direct heating mode, significant heat losses are observed as a result of the fact that the coolant vapor stripped from the solent releases its condensation heat to the environment upon condensation in the evaporator.